Problem: $ { {-2} \times \left[\begin{array}{r}{4} \\ {1} \\ {-1}\end{array}\right] = {?} } $
Answer: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{r}{-2}\times{4} \\ {-2}\times{1} \\ {-2}\times{-1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{r}{-8} \\ {-2} \\ {2}\end{array}\right]}$